The present invention generally relates to the field of pyrotechnic initiators, and more particularly to a method of axially spinning an initiator subassembly to distribute pyrotechnic charge therein.
Pyrotechnic initiators have many uses in industrial and consumer applications. One important use is in triggering the inflation of airbags in motor vehicles. Significant efforts have been made in the automotive industry to reduce the cost of manufacturing reliable airbag initiators. One advance has been the use of liquids and slurries in loading pyrotechnic charges into the initiators. As shown in U.S. Pat. No. 5,686,691 to Hamilton et al., it is known to load a slurry charge into a conventionally cup-shaped charge can, and to directly affix such a loaded can onto a header assembly so that the charge comes into contact with the header surface and bridgewire. A slurry may also be loaded into an initiator subassembly with the aid of a charge sleeve, as is taught in applicant""s co-pending U.S. application Ser. No. 09/733,755 by Avetisian et al., which was filed on Dec. 8, 2000 and entitled xe2x80x9cPyrotechnic Initiator with a Narrowed Sleeve Retaining a Pyrotechnic Charge and Methods of Making Same.xe2x80x9d
Loading a slurry directly into the charge can, however, poses drawbacks and difficulties relating to loading and proper retention of the charge against the bridgewire and the need for consolidation limits the range of suitable charge formulations. Loading a slurry without consolidation also poses drawbacks and difficulties in evenly loading the charge and in obtaining a dried slurry charge that contains a minimum of voids in the region of the bridgewire. If a slurry charge is loaded and not subjected to a consolidation force, there may be irregularities, uneven distribution, and excess voids in the region of the bridgewire, all of which may result in less reliable and predictable performance of the initiator. A centrifuge process may be used to distribute slurries evenly, however, this is a very costly process both in terms of initial investment and production maintenance. Vibratory and ultrasonic consolidation techniques are also known, however, they are not as reliable. Also, a tool may be used to tamp down the slurry (preferably when it is neatly dried), but this may be more difficult to do since the degree of slurry dryness must be accurately known, and the slurry may stick to the tool when it is wet. It is believed that heretofore, a method of axially spinning an initiator subassembly to distribute a pyrotechnic charge therein has never been utilized to address any of the foregoing problems.
In accordance with the present invention, an initiator subassembly is axially spun on its long axis (i.e., around the axis of the initiator subassembly that is perpendicular to the surface of the header assembly) to distribute pyrotechnic charge therein. This axial spinning is preferably done during the distribution of a slurry charge into the initiator subassembly; also, it may be done while an ignition charge is still in a slurry state, and/or it may be done while a separate output charge is still in a slurry state.